Fuel Pump Check Valve

[Jeff G 78]

I resurrected my '78 280Z after a 10-1/2 year nap in preparation of my move from Michigan to Arizona.  Back when I was driving it 10+ years ago, it had an issue that I never fixed.  The car fires right up minutes to hours after shutting it off, but after an overnight park, it takes 20 - 30 seconds of cranking before it chugs to life.  It usually coughs a few times and stalls after doing nothing for the first 20 or so seconds of cranking.  The next crank does the trick and once it starts, it runs perfectly.  I'm pretty sure it's due to a bad fuel pump check valve and normally, it would be a simple inconvenience, but in exactly two weeks, my Z gets picked up by a flatbed and transported to a depot where they will load it onto a car hauler along with my Porsche and my wife's FJ Cruiser for the trip to Arizona.  Knowing how car haulers work, it could need to be loaded and unloaded a few times to get other cars on or off along the way across the country.  I'm worried that the battery or starter might take a dump if they can't get it started or have to do it numerous times.

This move all happened very quickly and I was completely unprepared to deal with my Z cars and all my parts this quickly.

Is there a simple fix I can do to fix the pressure bleed-off?  I have almost no time to diagnose or experiment.  Is there an in-line check valve I could add somewhere?  Is it always at the pump, or are there other places the pressure could bleed off?

Thanks all and keep an eye out for a car hauler with my 517 Lt Gold Datsun, my silver 911 and my wife's tan FJ Cruiser aboard.  They should be heading West in mid to late March.  The hauler company says it will take 1-2 weeks to get there. 

[Jeff G 78]

Okay, I found an old thread showing that the check valves that screw into the pump are NLA.  I then found inline check valves.  Where can I install one of these?  Does it have to go between the tank and the pump, or can it go between the filter and the fuel rail?  It seems like it would have to go before the pump.  I'm guessing the pump loses prime which is why it takes so long to start.  Has anybody installed an inline check valve and if so, where did you put it?

https://www.amazon.com/Automotive-leader-Return-Petrol-Aluminium-Accessories/dp/B07GYMDN4F/ref=sr_1_8?dchild=1&keywords=5%2F16"+fuel+check+valve&qid=1614656494&sr=8-8

 

[EuroDat]

Jeff, I have a couple NOS, but I don't think you would get it in time for your move. 

I will have a look tonight. They are for a Mercedes bosch system, but it is more or less the same. You can't tell the difference when they are next to each other. My holds 2bar for more than three weeks.

[Jeff G 78]

7 hours ago, EuroDat said:

Jeff, I have a couple NOS, but I don't think you would get it in time for your move. 

I will have a look tonight. They are for a Mercedes bosch system, but it is more or less the same. You can't tell the difference when they are next to each other. My holds 2bar for more than three weeks.

Thanks Chas.  I appreciate the offer, but I agree that we don't have time.  Do you have a part number by any chance and a picture of yours?  Maybe I can find one locally or on Amazon.  I know there used to be a Volvo one, but those seem to be NLA as of 10+ years ago just like the Nissan OE one.

EDIT:  I found something on Amazon that is interesting.  It's a Bosch fuel pump check valve https://www.amazon.com/Bosch-1587010539-Fuel-Check-Valve/dp/B001CO2MYK and one of the reviews said that it was a direct fit for his 1975 Datsun 280Z.  The picture shows a threaded inlet though.  Isn't the OE check valve only threaded on the pump side and barbed on the inlet side?

I don't think it would arrive in time anyways even if it's the right one.  Amazon shows it arriving around the time the car ships.

Edited March 2, 2021 by Jeff G 78

[Captain Obvious]

The original check valve is screwed into the outlet side of the pump. So in "circuit" it's installed between the pump and the rail, not between the tank and the pump.

That said, for a quick fix, I think you could put something right before or after the filter. Putting something up in the engine compartment would certainly be faster and easier than dealing with anything underneath the car back by the tank.

Another option might be to do a (simple?) wiring modification so that the fuel pump is always running with the key in the ON position? Wouldn't have the safety feature of shutting off the pump in the event of a collision, but you would just hope the movers don't get involved in a big pileup with the car loading it onto the trailer.     I'm thinking that would allow the fuel pump to prime like the newer cars do. Just tell the movers to turn the key to ON and count to five before trying to start the engine?

[Jeff G 78]

37 minutes ago, Captain Obvious said:

The original check valve is screwed into the outlet side of the pump. So in "circuit" it's installed between the pump and the rail, not between the tank and the pump.

That said, for a quick fix, I think you could put something right before or after the filter. Putting something up in the engine compartment would certainly be faster and easier than dealing with anything underneath the car back by the tank.

Another option might be to do a (simple?) wiring modification so that the fuel pump is always running with the key in the ON position? Wouldn't have the safety feature of shutting off the pump in the event of a collision, but you would just hope the movers don't get involved in a big pileup with the car loading it onto the trailer.     I'm thinking that would allow the fuel pump to prime like the newer cars do. Just tell the movers to turn the key to ON and count to five before trying to start the engine?

Thanks Cap!  Just thinking out loud here...  If the check valve is at the pump outlet, then when it works, the supply line stays full of fuel.  With a check valve at the filter in the engine bay, the rail would stay pressurized as it should, but would the pump still lose prime and cause the same issue, or would there be enough fuel pressure to fire the engine and then keep it running while the line fills?  Adding a universal in line check valve is super simple and cheap.  They are about $10.  I'll try that first and see if it works.

[Captain Obvious]

Yes, when the check valve is working, then everything after the pump stays full of fuel and pressurized. Supply line from pump the engine bay, filter, rail, injectors... Everything between the pump and the pressure regulator.

And yes, if you put the check valve up in the engine compartment, then you will not have pressure in the line between the pump and the engine bay, but everything else should be pressurized.

I'm not sure the problem is the pump losing prime. I've found that if you disconnect the supply line to the pump, fuel comes out. Implication being that the pump is gravity primed. I'm thinking that maybe the fuel is "siphoning" out of the rail somehow to achieve an equilibrium point where everything is even. That point may not be as low as the pump, but it might be lower than the rail. If that's the case, you would have to run the pump to refill the rail, but the pump itself has not lost prime.

In other words, I'm thinking that the check valve does two things:

1) It keeps everything pressurized
2) It prevents "backflow" through the system that would allow the rail to drain from gravity?

Just a theory.

[Captain Obvious]

Oh, and I took a quick look at the wiring diagram for the 78.

There are two relays up in the engine compartment that deal with the fuel pump. The "fuel pump control relay" (which has five wires) and the "fuel pump relay" which has four.

If you pull the connector completely off the relay with five wires, there should be two W/B wires leading into the connector. Short those two W/B wires together and it disables the interlocking. The fuel pump should run any time the key is in the ON position. Let it hanging off the relay with just those two wires shorted together and put some tape on it?

As a quick alternative, that might get you through the time crunch?

However, I just took a quick look... If you're going to do this mod, let me know beforehand and I'll look into it a little more thoroughly.

Edited March 2, 2021 by Captain Obvious

[Captain Obvious]

Another simpler option would be to simply disconnect the oil pressure sender connector and let it hang. The fuel pump will run any time the key is ON..

Of course, the oil pressure gauge won't work with that connector off, but for the trip to AZ, it would be OK.

[Jeff G 78]

I'll try the oil pressure sender wire first.  That's super easy.  I think I'll install an inline check valve between the filter and rail and see if that works.  If so, I won't have to deal with any electrical.  

I got the quote back to ship the car via the same transport company as my other two cars (Company pays to move two, so I have to pay for the Z).  The quote came back really high, so I'l likely going to use another carrier.  $1813 to move the Z on an open carrier!  I got another quote for $1200 and I'm awaiting others to come back.

[Zed Head]

FPR's tend to leak down also.  It will cause the same extended cranking problem.  And non-functioning cold start valves will add some cranks.  

[Jeff G 78]

2 minutes ago, Zed Head said:

FPR's tend to leak down also.  It will cause the same extended cranking problem.  And non-functioning cold start valves will add some cranks.  

I think I have a few regulators, though, I'd rather not disturb the old hoses right now.  The car fires right up even after several hours, so it's a bleed down issue of some kind for sure.  The cold start seems to work fine.